1. Field of the Invention
The present invention relates to a heat exchanger and an evaporator using the heat exchanger.
Priority is claimed on Japanese Patent Application No. 2003-104105, filed Apr. 8, 2003, the content of which is incorporated herein by reference.
2. Description of the Related Art
As a method of supplying a fuel gas to a fuel cell, in some cases, a raw fuel of a liquid containing hydrocarbons such as methanol or gasoline is reformed into a hydrogen-rich fuel gas (hereinafter abbreviated as hydrogen-rich gas) by a reforming system, and this hydrogen-rich gas is supplied as a fuel gas for the fuel cell.
In this reforming system, a liquid fuel (raw material) consisting of a mixed solution of a raw fuel and water is evaporated by an evaporator to be converted into a raw fuel gas, and the raw fuel gas is supplied to a reformer together with a reforming air to cause a reforming reaction. Then, the raw fuel gas is reformed into a hydrogen-rich gas by the reforming reaction. The evaporator of this type is disclosed in, for example, Japanese Unexamined Patent Application, First Publication No. 2001-135331.
Incidentally, there is an evaporator of a heat exchanger type. The evaporator generates a raw fuel gas by flowing a heating gas and a fuel gas through a heating gas passage and a heated gas passage, which are partitioned by a partition plate or the like, and transferring heat of the heating gas to the liquid fuel to evaporate the liquid fuel.
However, in the conventional evaporator of the heat exchanger type consisting of such a structure, since both ends of the partition plate are fixed, the partition plate thermally expands when used under a high-temperature environment. As a result, thermal stress is caused in portions where both the ends of the partition plate are fixed. In order to allow the partition plate to withstand this thermal stress, thickness of components to which the thermal stress is applied has to be increased to improve rigidity, which causes an increase in weight. In addition, since a heat capacity of the evaporator increases following the increase in weight, there is also a drawback in that a longer start-up time is required.
In addition, a method of using bellows or the like in order to relieve thermal stress is also possible. However, new problems occur in that the number of components is increased, the structure of the evaporator becomes complicated, and manufacturing costs are also increased.